1. Field of the Invention
This invention relates to methods of and apparatus for processing binary data.
More particularly, the invention is concerned with the recovery of socalled framing information from an incoming stream of binary data.
2. Description of the Prior Art
Consider, for example, a color television camera control system in which control and information signals are coded to produce blocks of bits which are put together to form a continuous stream of binary data which is then supplied over a transmission link such as an audio pair or radio link to a remote television camera. At the camera the incoming stream of binary data must be decoded to derive the control and information signals. The steps necessary to do this include recovery of the clock signal, and then framing, this latter term meaning identification of which bits in the stream of binary data form the required blocks of bits representing the control and information signals. Recovery of the clock signal is generally quite simple and may use a phase lock technique. This technique may fail if the data is all "0" or all "1", but this problem can be overcome fairly simply, for example, as will be described below.
A more difficult problem is the framing. In one proposed control system the data are produced in blocks of eight bits, each block having in addition a parity bit, so that the transmitted blocks are each of nine bits. At the receiver the incoming stream of binary data is tested successively in each of the nine possible framing positions to see which position most accurately regenerates the received parity bits. However, it is possible in some circumstances for the lock-in to occur incorrectly, and this possibility becomes more likely in the quite common situation where the incoming stream of binary data contains errors after transmission over a noisy link.